The gripping fourth installment in an epic series about Furnace - a terrifying, underground prison for teenagers - now with a stunning new cover treatment.

Alex thought that escape was impossible. He was wrong.

We broke out of Furnace but we're still not free. The city is in lockdown - roads sealed, police everywhere. And there are worse things here: creatures of death sent to bring the world to its knees.

I'm turning into one of them, into a monster. To put an end to this blood-crazed madness I have to travel into the heart of darkness. I have to find Alfred Furnace before he finds me.

Soon the whole world will be a prison.

Action-packed, gritty and gruesome - this is the perfect read for thrill-hungry teens. With striking new covers that really bring these chilling stories to life.